Traveling-wave type electron tube utilizing interaction between beam and te20 waveguide mode



Sept. 3,

Filed July 2l, 1965 YOSHIKAZU MIYAMOTO TRAVELING-WAVE TYPE ELECTRON TUBE UTILIZING INTERACTION BETWEEN BEAM AND TE2O WAVEGUIDE MODE 2 Sheets-Sheet 1 INVENTOR Voslvi/(azu Mit/zumal@ modern Sept. 3, 1968 YosHlKAzU MwAMoTo 3,400,297

TRAVELING-WAVE TYPE ELECTRON TUBE UTILIZING INTERACTION BETWEEN BEAM AND TEZOWAVEGUIDE MODE n 2 Sheets-Sheet 2 Filed July 21, 1965 MWI,

United States Patent O 3,400,297 TRAVELING-WAVE TYPE ELECTRON TUBE UTI- LIZING INTERACTIUN BETWEEN BEAM AND TEN WAVEGUIDE MODE Yoshikazu Miyamoto, Suginami-ku, Tokyo-to, Japan, assignor to Kabushiki Kaisha Hitachi Seisakusho, Tokyoto, Japan, a joint-stock company of Japan Filed July 21, 1965, Ser. No. 473,672 Claims priority, application Japan, July 27, 1964, 39/42,040 4 Claims. (Cl. S15-3.5)

ABSTRACT F THE DISCLOSURE A traveling lwave tube which has a slow-wave circuit structure of high impedance. The fundamental wave becornes the forward wave, and the construction of the device is so that a rectangular wave-guide of the transmission mode, eg., a TE-o mode, has a cross section of electric fields of mutually opposite direction and is in bent and folded configuration.

This invention relates to traveling-wave tubes and more particularly to a new traveling-wave tube having a slowwave circuit structure of high impedance wherein the fundamental wave becomes the forward wave and a construction wherein a rectangular waveguide having, for example, a T1520 transmission mode which in the cross section of the waveguide has electric fields of mutually opposite direction is in a bent and folded configuration.

In general, the construction of the slow-wave circuit of a traveling-wave tube is required to be simple and heat resistant and, moreover, have high interaction impedance.

Heretofore, in a high-power, traveling-wave oscillator tube or amplifier tube, practical use has been made of a so-called interdigital circuit in which two comb structures are combined in order to obtain electromagnetic waves of low-phase velocity, but the construction of such tubes has been complicated. Furthermore, in tubes of the type consisting of rectangular waveguides bent and folded, in the axial direction, the coupling impedance of the electromagnetic waves and electrons is low.

In such a circuit, if the phase difference of the electromagnetic waves propagating in the axial direction thereof is denoted by 0 for each length L of period along the electromagnetic wave propagated path of the circuit, an electromagnetic wave of a phase difference H-i-fr (space harmonic wave) will exist together with an electromagnetic wave of a phase difference 0-1r (fundamental wave).

In a conventional bent circuit, since an electromagnetic wave of phase difference of 0-1r becomes a backward wave, the 0|1r component to become a traveling-wave is utilized in tubes such as traveling wave tubes.

By this method, however, the impedance acting on the electrons is low in comparison with the fundamental wave, and an amply high power cannot be produced.

It is an object of the present invention to provide a traveling-wave tube of simple construction and high efficiency wherein the above described difficulties and deficiencies are overcome.

According to the present invention, briefly stated, there is provided a slow-wave circuit wherein, through utilization of the folded line in the axial direction of a rectangular waveguide having within its cross section electric fields of mutually opposite direction, for example, a TE20 mode, the coupling impedance is caused to Ibe the same as that of the fundamental wave, and the phase difference 'between the electroma-gnetic wave and the electrons at the interaction gap is caused to be 0.

More specifically, according to the invention there is 3,400,297 Patented Sept. 3, 1968 ice f provided a traveling-wave type electron tube comprising a waveguide for propagation of an electromagnetic wave of a mode having electric fields of mutually opposite directions in the waveguide cross section, said waveguide being bent and folded in its axial direction in a corrugated configuration resembling a rectangular wave train and, moreover, having a transversely staggered form whereby half portions of the transverse folds thereof are alternately overlapped as viewed in the axial direction, the waveguide parts so overlapped being respectively provided with small holes alined along a straight line thereby to enable an electron beam to advance in a straight line.

The nature, principle, and details of the invention will be more clearly apparent from the following detailed description `when read in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective `view showing one example of a slow-wave circuit of know type;

FIG. 2 is a fragmentary sectional view for description of the phase at an electron beam passage hole of an electromagnetic wave passing through a conventional slowwave circuit;

FIGS. 3 and 4 are diagrams for description of electromagnetic waves in the transverse direction of waveguides;

FIG. 5 is a schematic diagram for description of the principle of the traveling-wave tube of the invention;

FIG. 6 is a perspective view showing a preferred embodiment of the invention;

FIG. 7a is a schematic diagram of another embodiment of the invention, and IFIGS. 7b through 7e are crosssectional diagrams of each portion of the embodiment shown in FIG. 7a; and FIG. 8 is a schematic diagram of the traveling-wave tube of the invention.

Referring to FIG. 1, there is shown a perspective view of a conventional slow-wave circuit of the folded line waveguide type, in which a waveguide for transmitting TEM, mode waves is successively bent and folded for each period L to form a corrugated structure. The dotted line indicates the circuitous path of wave propagation, and the cross hatched circular parts indicate small holes formed in the E-planes of the waveguide so as to enable electrons to travel in a straight path in the axial direction.

FIG. 2 shows a fragment of this folde-d line in section taken along the axial direction, and FIG. 3 indicates the electric field distribution of a TEN, mode in the transverse direction within the waveguide. An electromagnetic wave of a T1310 mode of an electric field distribution as indicated in FIG. 3 propagates within the waveguide interior in directions indicated by the arrows in FIG. 2, and, for each folding period L, the phase angle of the guide assumes a difference of degrees. That is, at the positions of the holes P1 and P2, the phase angle is reversed, and the fundamental `wave becomes a backward wave. At the same time, the electron beam is not subject to the interaction thereof, and a so-called space harmonic wave component forms an interaction field with respect to the electrons.

With the above considerations in view, the present invention contemplates provision of a slow-wave circuit wherein the interaction field with respect to the electrons is strong, and the fundamental wave becomes a forward wave.

Referring to FIG. 4, there is indicated an electric field distribution in the transverse direction of a rectangular waveguide of 'Tl-E20 mode. According to the present invention, an electric field distribution of T1320 mode of this character is utilized, and a waveguide for transmitting TF2@ mode electromagnetic waves is bent and folded in the axial direction of the waveguide, similarly as in the conventional case, and, moreover, with the use of not only E-bends but also H-bends so as to cause overlapping of approximately halves of E-planes in their transverse direction.

FIG. 5 shows a sectional view taken along the bent waveguide axis and transverse direction in this case, only the waveguide parts cut by the sectional plane being shown. As shown, transverse halves of the waveguide are overlapped in staggered arrangement. Quarter-width points are designated by reference characters P1 and Pla, PZ and Pza, and so forth. Then, an E+ electric field at point P1 is inverted to E- at point P2asimilarly as in the case of a TEM, mode. On the other hand, an E- electric field at point Pla becomes E+ at the point P2, and thereafter the electric field directions change in the same manner.

Therefore, if the electron passage holes are formed at positions in the direction of the E+ electric fields as at P1, P2, etc., the phase difference in one period length L of the bends will become 0. That is, this is a fundamental forward wave. By thus staggering the transverse positions of the waveguide and passing the electrons through holes provided at points corresponding to points, P1, P2, etc., the electrons can be subjected to the interaction of amply strong electric fields.

Referring to FIG. 6 showing in perspective view one example of a slow-wave structure embodying the invention, the slow-wave structure is formed of a periodically folded strip line, which propagates an electro-magnetic wave of T1320 mode and comprises a plurality of waveguide portions 1 and a plurality of waveguide portions 2 and 4 perpendicularly connected to the waveguide portions 1 alternately.

The waveguide portions 1 are arranged in parallel along the electron beam axis and suitably spaced from each other. The waveguide portions 2 are formed of an H-plane bend, which is bent in wedge-shape in H-plane and the waveguide portions 4 are also formed of H-plane bends, bent in opposite direction with respect to the waveguide portions 2. In the above-described structure, as viewed in the axial direction, the waveguide portions 2 and 4 are mutually overlapped with a half-width thereof at the half-Way, and holes 3 for electron beam are formed in the waveguide portions 2 and 4, respectively, at one quarter-width positions in the mutually overlapping parts of the respective waveguide portions 2 and 4, so as to enable the electron beam to travel along a straight line of aligned holes 3.

Another embodiment of this invention is indicated in FIG. 7a, which comprises a plurality of blocks closely arranged in a common axis. Each of the blocks consists of metal plates 10, 11, 12 and 13 successively overlapped, the

cross-sectional views of which are shown in FIGS. 7b, 7c, 7d and 7e, respectively. The metal plates 10 and 12 respectively have an opening 14 for passing a microwave therethrough and one hole 15 at the center thereof for passing the electron beam, and the metal plates 11 and 13 have cutout parts 16 and 17, respectively, which form H- plane bends. The above-described embodiment forms a wave path when the metal plates are successively piled to an extreme degree in the axial direction which is equivalent to such a configuration of the folded waveguide shown in FIG. 6.

By selecting the dimensions of the various parts of the waveguides shown in FIGS. 6 and 7a to suit the TE20 mode transmission of the electromagnetic wave used, a slow-wave circuit suitable for the wavelength used can be produced.

Referring to FIG. 8 showing a traveling-wave type electron tube composed of the slow-wave structure according to the invention, the entire tube is constructed of an electron gun for forming and projecting an electron beam, an electron beam 21 emitted from the electron gun, a collector 22 for collecting the electron beam, the slow-wave structure 23 as shown in FIG. 6 having a micro-wave input portion 24 and a micro-wave output portion 25, an air-tight vessel 26 accommodating the electron gun 20,

theV slow-wave structure 23 and the collector 22 in vacuum. The reference numeral 28 is a hole or aperture for allowing the electron beam to pass therethrough and is provided in each of a plurality of the H-plane bends.

In the traveling-wave tube of the above-mentioned structure, the electron beam 21 emitted from the electron gun 20 passes through the holes or aperture 28 formed at positions in the direction of the E+ electric field and interacts with the fundamental forward wave component of the micro-wave introduced in the input portion 23, transmitting along the slow-wave structure 23. Therefore, the 4micro-wave is efficiently provided with electro-magnetic energy from the electron beam, and is taken out from the output portion 25 of the waveguide.

As described above, the present invention provides a slow-wave circuit of simple construction in which the fundamental wave becomes a forward wave, and which has a high impedance characteristic and high electron tube efficiency. Accordingly, the same operational objects can be achieved with a slow-wave circuit of much shorter circuit length than a conventional circuit. For this reason, a traveling-wave tube, particularly a traveling-wave tube for the millimeter wave region, in which this slow-wave circuit is used, has various advantages such as the miniature size of electromagnets required for focusing the electron beam.

While in the foregoing description, a traveling-wave tube has been considered by way of example, it will be obvious that by using the space harmonic waves of the slow-wave circuit according to the invention, this circuit can be used also in backward wave tubes.

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claim.

What is claimed is:

1. A traveling-wave tube comprising: waveguide means having a folded wave path which is folded in E-plane in a rectangular wave fashion to define mutually opposedly adjacent wave path portions, said mutually oppositely adjacent wave path portions being bent alternately in opposite fashion in H-plane so as to be aligned with each other with a half-width overlap at the half-Wave thereof; a plurality of aligned apertures provided in said waveguide means to define a straight path therethrough, transversely crossing mutually overlapping parts of said respective wave path portions at a half-way and a quarter- Width point thereof, respectively; means for introducing an electro-magnetic wave into said waveguide means to allow said wave to propagate along said wave path in the state of TEZD mode thereof; and means for projecting an electron beam through said aligned apertures along said straight path to allow the electron beam passing therethrough to electro-magnetically intercouple with the electro-magnetic fields generated by said wave within the respective wave path portions, whereby said electron beam interacts with a fundamental forward wave component of the introduced electro-magnetic wave.

2. The traveling-wave tube according to claim 1, wherein said waveguide means is formed of a plurality of metal plates provided with hollow paths and piled up so that the respective hollow paths may form said wave path and straight line.

3. The traveling-wave tube according to claim 1, wherein said waveguide means is formed of a folded waveguide having an upper and a lower wall parallel to the H-plane, said waveguide being folded in E-plane to define mutually oppositely aligned waveguide portions, said waveguide portions being bent in H-plane alternately in opposite direction so as to provide a staggered alignment; and wherein said apertures are provided in the upper and lower walls of the respective waveguide portions to provide a straight path transversely crossing the overlapping parts of the waveguide portions.

4. A slow-wave structure used' for a traveling-wave type electron tube having an electron gun for projecting out an electron beam and a collector for collecting the electron beam comprising: a periodically twisting waveguide alternately crossing over and extending along the electron beam axis, a plurality of waveguide portions of said waveguide being successively arranged to cross over the electron beam axis and being bent in H-plane in opposite fashion to each other and alternately arranged in the axial direction, so as to alternately overlap each other with a half-width thereof as viewed in the axial direction; and a plurality of apertures provided in the walls of said respective waveguide portions at one quarter-width positions thereof in their overlapping parts so as to enable the electron beam to transversely cross mutually overlapping parts of said respective waveguide portions and to pass therethrough to said collector, whereby the electron beam interacts with a fundamental forward electro-magnetic wave of T E20 mode introduced in said slow-wave structure.

References Cited UNITED STATES PATENTS 2,532,545 12/ 1950 Everhart 315-39.73 2,770,780 11/ 1956 Warnecke et al. 333-31 2,925,567 2/ 1960 Eichin et al S15-39.3 X

HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, J R., Assistant Examiner. 

